32 MARVELS OF FISH LIFE 
photograph was again taken by a front light, and he is 
stili revealed by his dark back and white under-surface. 
The stone-like markings in themselves were insufficient 
to conceal him. In the bottom illustration the fish 
was photographed by a top light only, and now we see 
how effectively the markings seen on a uniformly shaded 
fish conceal him. 
The perch illustrates the value of reed-like markings, 
for, in addition to his dark back and white under-surface, 
he is crossed by five or more bars, as shown in the 
illustration of a perch photographed in a tank by a 
front light. When seen under natural conditions, the 
dark back and white under-surface again become of a 
uniform shade. This uniform shade in itself would 
render the body of the perch conspicuous by interrupting 
the reed scenery beyond. But the markings break up 
the uniformly shaded body of the fish, and at the same 
time merge with the pattern formed by the reeds. 
Water has a bluring effect, and when a perch is seen 
through two or three feet of this medium, the bar mark- 
ings do not appear to be on the fish at all, but to be 
part of the reeds themselves. As a result, the eye of 
the observer is not arrested by the form of the fish, 
but is carried to the reeds beyond, and thus the perch 
escapes detection. 
Thayer, the American artist and naturalist, in his 
exceedingly interesting book “ Concealing Coloration in 
the Animal World,” has brought into prominence this 
principle, of how the dark back and lighter under-parts 
